The invention relates to a premix burner arrangement as well as to a method for operating the same, comprising a pilot fuel feeding means for operating a combustion chamber of a gas turbine arrangement, a premix burner housing, wherein at least one fuel addition unit as well as supply air openings have been provided in such a way that gaseous and/or liquid fuel can be mixed with combustion supply air inside the premix burner housing and form a fuel/air mixture, which exits from the premix burner housing downstream in the direction towards the combustion chamber positioned after the premix burner arrangement and which can be ignited inside the combustion chamber in the form of a spatially largely stationary flame.
A premix burner of the above mentioned type is the subject of German Offenlegungsschrift DE 196 54 009 A1. The known premix burner comprises a conically expanding housing, within which a fuel/air mixture is formed by providing air inlet slits in an appropriate manner. Furthermore, a swirl generator is provided downstream, which provides the fuel/air mixture, after the latter passes the premix burner, with a specific, critical swirl value necessary for a spatially stabile flame that forms inside the combustion chamber after the ignition of the fuel/air mixture. The start-up or ignition of such premix burners requires a targeted feeding of the pilot gas into the premix burner. After igniting the pilot gas fed into the premix burner, a diffusion flame for igniting the fuel/air mixture produced axially in the premix burner forms, whereby said fuel/air mixture in the ideal case forms a spatially stable flame front near the backflow zone. The pilot gas feeding means also helps in increasing the flame stability in the lower partial load range of the premix burner, i.e., under operating conditions in which the premix burner is operated with lean mixtures.
Special attention in the operation of such premix burner systems is paid to the waste gas values occurring during the combustion, and in particular to NOx emissions, which, however, significantly increase during the additional piloting and resulting diffusion flame as a result of rising flame temperatures.
In order to reduce NOx emissions, and for other reasons, premix burners with a subsequent mixing section as disclosed, for example, in EP 0 83 105 A2, have become known. Inside the mixing section that follows the premix burner, the fuel/air mixture is able to mix completely before the mixture is ignited in the combustion chamber. However, for the startup and also for operating conditions with only lean mixture supply, burner systems optimized in this manner require an actually known piloting means as used, in particular, in the lower partial load operation of gas turbine systems. Here also the additional pilot gas supply has a strong influence on the NOx emissions produced by the combustion, in spite of the additional mixing section.
The invention is based on the objective of constructing a premix burner arrangement comprising a pilot fuel feeding means for operating a combustion chamber of a gas turbine arrangement, a premix burner housing, wherein at least one fuel addition unit as well as supply air openings have been provided in such a way that gaseous and/or liquid fuel can be mixed with combustion supply air inside the premix burner housing and form a fuel/air mixture, which exits from the premix burner housing downstream in the direction towards the combustion chamber positioned after the premix burner arrangement and which can be ignited inside the combustion chamber in the form of a spatially largely stationary flame in such a way that on the one hand the NOx emission values occurring during the combustion should be decisively reduced, and on the other hand the stability of the flame forming inside the combustion chamber should be maintained or optimized. The constructive measures necessary for this should be as economical as possible and also should be retrofittable for premix burner arrangements already in operation.
The method discloses a method according to the invention for operating a premix burner arrangement with pilot fuel feeding means. Characteristics that advantageously further develop the concept of the invention are the subject of the secondary claims and specification, in particular in reference to the exemplary embodiments.
According to the invention, a premix burner arrangement with a pilot fuel feeding means for operating a combustion chamber of a gas turbine arrangement according to the preamble of claim 1 is constructed so that outside of the premix burner, a catalyzer unit is provided, through which the pilot fuel feeding is performed in such a way that a pilot fuel/air mixture flows through the catalyzer unit and can be converted at least in part catalytically in it and flows as a mass flow that stabilizes the flame into the combustion chamber.
The term xe2x80x9cpremix burnerxe2x80x9d relates to a premix burner arrangement composed of a preferably conically constructed premix burner housing containing at least one fuel injection means as well as supply air openings, through which flows supply air for forming a fuel/air mixture inside the premix burner housing, a swirl generator that follows the premix burner housing downstream, as well as an optional mixing section following the swirl generator.
Regardless of whether the premix burner arrangement is provided with a mixing section that follows the swirl generator, the concept according to the invention moves away from the actually known pilot gas feeding means inside the premix burner, for example, using a pilot gas lance, and principally provides for a catalytic conversion of a pilot fuel even before the latter reaches the area of the combustion chamber. By means of the at least partial catalytic conversion of the supplied pilot fuel, that is mixed with air prior to entering the catalyzer unit and flows through the catalyzer unit in the form of a pilot fuel/air mixture, at least a large part of the pilot fuel is converted thermally and/or catalytically, creating a mass flow entering the combustion chamber, said mass flow consisting in the form of an ignitable gas mixture or alternatively as a type of hot gas flow. The mass flow having the form of an ignitable gas mixture then directly reaches the area of the flame front inside the combustion chamber, whereupon it is ignited and creates only the smallest of NOx emissions. Even in the case of a complete chemical conversion of the pilot fuel, which results, for example, in a mass flow in the form of a hot gas, preferably consisting of the full oxidation products CO2 and H2, only the smallest portions of NOx are created.
Since, with respect to the substance, the catalytic conversion of the pilot fuel takes place completely separate from the fuel/air mixture forming inside the premix burner, the pilot fuel can be freely selected with respect to type and volume of supply through the catalyzer unit.
The catalyzer unit preferably is arranged downstream on the premix burner, immediately before entering the combustion chamber or downstream from the mixing section following the swirl generator in such a way that the catalyzer unit surrounds the mixing section at least in part in a circular manner. It was found to be especially advantageous for a catalyzer unit arranged circularly around the mixing section that the catalytically converted mass flow flowing from the catalyzer unit into the combustion chamber is able to decisively stabilize the flame front forming inside the combustion chamber in the area of the backflow zone. The catalytically converted mass flow preferably meets the flame front that forms in paraboloid manner inside the combustion chamber in edge regions, which makes it possible, as confirmed experimentally, to increase the stability of the flame. This is true in particular for an operation with lean fuel/air mixtures, as is the case in the lower partial load range.